Vacuum, atmospheric and controlled environment processing for applications such as associated with manufacturing of semiconductor, LED, Solar, MEMS or other devices utilize robotics and other forms of automation to transport substrates and carriers associated with substrates to and from storage locations, processing locations, or other locations. Such transport of substrates may be moving individual substrates, groups of substrates with single arms transporting one or more substrates or with multiple arms, each transporting one or more substrate.
In some applications it is advantageous to transport and process more than one substrate in parallel. Here, throughput of a given tool may be increased without a proportionate increase in footprint and cost. In addition, such applications may require the ability of the transport robot to quickly swap processed substrates for unprocessed substrates at a given process module, improving utilization of the module and throughput of the system. A problem arises in such applications where four substrates (two processed, two unprocessed) are handled with a fast swap where the arms of the robot are required to pass over the substrates or where a bridge is used on one of the two substrate end effectors to allow it to pass over the other two substrate end effector. If the upper structure includes a rotational joint which passes over the lower structure and/or a wafer carried by the lower structure, contamination is possible. See U.S. Pat. No. 6,315,512 incorporated herein by this reference. A bridge associated with the upper structure can be unwieldy, cumbersome, and difficult to tune. See U.S. Pat. No. 5,151,008 incorporated herein by this reference. A substrate transport apparatus in accordance with various examples of the invention has no upper rotating joins passing over a lower wafer and a bridge is not required or needed. Accordingly, there is a desire to provide a substrate transport robot that does not require such a bridge for a given range of transport applications with minimized transport and swap times.